Control of engine valve timing can be important for improving engine performance and facilitating a variety of other machine operations. For example, proper valve timing can help improve engine power output and fuel efficiency. Further, variable valve timing can be used to facilitate other machine operations such as braking of highway vehicles and control of exhaust system operation through regulation of combustion byproduct production and/or control of exhaust system temperature.
Generally, engine valve timing is selected to optimize certain engine performance parameters such as power output, fuel efficiency, and/or exhaust emissions. However, to facilitate machine operations such as braking or control of exhaust temperature, it may be desirable to change valve timing only when these operations are desired. For example, elevated exhaust temperature may be periodically needed to regenerate diesel particulate filters (DPFs). However, since the production of hot exhaust gases may decrease power output and/or fuel efficiency, it would be beneficial to have a valve actuation system that can switch to a hot, DPF regeneration mode periodically and temporarily when needed.
One valve-timing control system is described in U.S. Pat. No. 6,564,763, which issued to Shiraishi on May 20, 2003 (hereinafter the '763 patent). The '763 patent includes an engine and control mechanism for varying the opening and closing time of intake and exhaust valves. Further, the '763 patent provides methods for heating cold catalysts by controlling valve timing.
Although the system of the '763 patent may provide suitable valve timing control for many engines, the system of the '763 patent may have some drawbacks. For example, the '763 patent does not provide systems or methods for alternatively selecting valve timing to effect braking or exhaust gas heating as desired. Further, the system of the '763 patent includes an electronic valve control mechanism but does not provide a method for ensuring consistent valve timing and optimum performance.
The present disclosure is directed towards overcoming one or more of the shortcomings of the prior art variable valve timing systems.